Bottom Line:
In this review, we analyse the impact of a population and evolutionary genetics approach on the study of insect behaviour.Our attention is focused on the model organism Drosophila melanogaster and several other insect species.In particular, we explore the relationship between rhythmic behaviours and the molecular evolution of clock and ion channel genes.

Affiliation: Department of Biology, University of Padova, Italy, Padova, Department of Biology, University of Padova, Padova, Italy.

ABSTRACTIn this review, we analyse the impact of a population and evolutionary genetics approach on the study of insect behaviour. Our attention is focused on the model organism Drosophila melanogaster and several other insect species. In particular, we explore the relationship between rhythmic behaviours and the molecular evolution of clock and ion channel genes.

f01: period ( per ) transgenes of Drosophilamelanogaster ( mel ) (black) and Drosophilapseudoobscura ( pseudo ) (light gray). H [25 aminoacid (aa)] and P (30 aa) domains represent the protein region immediatelyN-terminal to the repetitive region in both species. mps2 ,mps3 , mps4 and mps5 arechimeric melanogaster-pseudoobscura transgenes in which differentportions of the two mel and pseudo genes arecombined, so that to maintain or disrupt the conspecific coevolving aa blocks. Therepeat region corresponds to the threonine-glycine encoding repeat region(Thr-Gly) dipeptide run in D. melanogaster and to thepentapeptide run in D. pseudoobscura . Levels of rescue ofrhythmicity (% of rhythmic flies) for the different transgenes in aper01 genetic background and presence (+) or absence (-) of temperaturecompensation are indicated.

Mentions:
Later, we further extended our analyses to compare the Thr-Gly region from otherDrosophila species within the Drosophila andSophophora subgenera and found that this repetitive region exhibitsenormous variability in both DNA sequence and length in these species ( Peixoto et al. 1993 ). For instance, Drosophilapseudoobscura has approximately 35 copies of a 5-amino-acid degenerate repeat(rich in serine, glycine and asparagine or threonine), which appears to be derived throughreplicative slippage from a Thr-Gly repeat sequence. This corresponding repeat region inD. pseudoobscura is greater than 200 residues in length, which isapproximately four times longer than the repeat region of D. melanogaster ( Colot et al. 1988 ). Other species have very shortrepeats with little more than 10 residues ( Peixoto et al.1993 ). Moreover, in spite of the differences between the amino acid sequences ofthe repeats, their predicted secondary structures (a stretch of flexible turns thatseparates 2 globular domains) were conserved, suggesting that evolutionary and mechanisticconstraints shaped the PERIOD protein of these two species ( Costa et al. 1991 ). More importantly, a comparative analysis of theDNA sequences of the species under investigation indicated that the changes in length ofthe so-called “Thr-Gly variable region” were associated with amino acid replacements in themore conserved flanking sequences ( Peixoto et al.1993 , Nielsen et al. 1994 ). A Peixotoimmediately realised that this finding implied that the repeat length was co-evolving withthe flanking region to maintain the protein conformation of that region. To challenge thiscoevolution hypothesis, we designed a functional test in which several chimericper transgenes from D. melanogaster and D.pseudoobscura were generated; we used various chimeric junctions to maintain ordisrupt the species-specific contiguity of the “Thr-Gly repetitive region” with either allor part of the co-evolved 5’ flanking region that encodes the 55 amino acids immediatelyupstream of the Thr-Gly regions of the two species ( Peixoto et al. 1998 ). The analysis of the locomotor behaviours of the differenttransgenic flies provided dramatic experimental support for the coevolutionaryinterpretation: disrupting the coevolution of the repeat with its flanking region led to analmost arrhythmic clock, whereas maintaining the species-specific contiguity of the tworegions resulted in wild-type phenotypes. A partial disruption of the species-specificcontiguity generated a highly temperature-sensitive period, revealing a disturbance of thetemperature compensation of the clock ( Peixoto et al.1998 ) ( Figure ).

f01: period ( per ) transgenes of Drosophilamelanogaster ( mel ) (black) and Drosophilapseudoobscura ( pseudo ) (light gray). H [25 aminoacid (aa)] and P (30 aa) domains represent the protein region immediatelyN-terminal to the repetitive region in both species. mps2 ,mps3 , mps4 and mps5 arechimeric melanogaster-pseudoobscura transgenes in which differentportions of the two mel and pseudo genes arecombined, so that to maintain or disrupt the conspecific coevolving aa blocks. Therepeat region corresponds to the threonine-glycine encoding repeat region(Thr-Gly) dipeptide run in D. melanogaster and to thepentapeptide run in D. pseudoobscura . Levels of rescue ofrhythmicity (% of rhythmic flies) for the different transgenes in aper01 genetic background and presence (+) or absence (-) of temperaturecompensation are indicated.

Mentions:
Later, we further extended our analyses to compare the Thr-Gly region from otherDrosophila species within the Drosophila andSophophora subgenera and found that this repetitive region exhibitsenormous variability in both DNA sequence and length in these species ( Peixoto et al. 1993 ). For instance, Drosophilapseudoobscura has approximately 35 copies of a 5-amino-acid degenerate repeat(rich in serine, glycine and asparagine or threonine), which appears to be derived throughreplicative slippage from a Thr-Gly repeat sequence. This corresponding repeat region inD. pseudoobscura is greater than 200 residues in length, which isapproximately four times longer than the repeat region of D. melanogaster ( Colot et al. 1988 ). Other species have very shortrepeats with little more than 10 residues ( Peixoto et al.1993 ). Moreover, in spite of the differences between the amino acid sequences ofthe repeats, their predicted secondary structures (a stretch of flexible turns thatseparates 2 globular domains) were conserved, suggesting that evolutionary and mechanisticconstraints shaped the PERIOD protein of these two species ( Costa et al. 1991 ). More importantly, a comparative analysis of theDNA sequences of the species under investigation indicated that the changes in length ofthe so-called “Thr-Gly variable region” were associated with amino acid replacements in themore conserved flanking sequences ( Peixoto et al.1993 , Nielsen et al. 1994 ). A Peixotoimmediately realised that this finding implied that the repeat length was co-evolving withthe flanking region to maintain the protein conformation of that region. To challenge thiscoevolution hypothesis, we designed a functional test in which several chimericper transgenes from D. melanogaster and D.pseudoobscura were generated; we used various chimeric junctions to maintain ordisrupt the species-specific contiguity of the “Thr-Gly repetitive region” with either allor part of the co-evolved 5’ flanking region that encodes the 55 amino acids immediatelyupstream of the Thr-Gly regions of the two species ( Peixoto et al. 1998 ). The analysis of the locomotor behaviours of the differenttransgenic flies provided dramatic experimental support for the coevolutionaryinterpretation: disrupting the coevolution of the repeat with its flanking region led to analmost arrhythmic clock, whereas maintaining the species-specific contiguity of the tworegions resulted in wild-type phenotypes. A partial disruption of the species-specificcontiguity generated a highly temperature-sensitive period, revealing a disturbance of thetemperature compensation of the clock ( Peixoto et al.1998 ) ( Figure ).

Bottom Line:
In this review, we analyse the impact of a population and evolutionary genetics approach on the study of insect behaviour.Our attention is focused on the model organism Drosophila melanogaster and several other insect species.In particular, we explore the relationship between rhythmic behaviours and the molecular evolution of clock and ion channel genes.

Affiliation:
Department of Biology, University of Padova, Italy, Padova, Department of Biology, University of Padova, Padova, Italy.

ABSTRACTIn this review, we analyse the impact of a population and evolutionary genetics approach on the study of insect behaviour. Our attention is focused on the model organism Drosophila melanogaster and several other insect species. In particular, we explore the relationship between rhythmic behaviours and the molecular evolution of clock and ion channel genes.